N-valued optical logic architecture and method

ABSTRACT

An architecture for optical logic gates is presented in which N predetermined wavelengths of light are used to define data. This data is manipulated by N-valued optical logic gates based on a set of rules referred to as Song&#39;s switching algebra. The gates when connected end to end to produce optical circuits such as optical random access memory or an optical arithmetic logic unit.

FIELD OF THE INVENTION

[0001] This invention relates to optical logic and more particularly, tooptical computing using N wavelengths to represent N values.

BACKGROUND OF THE INVENTION

[0002] The development of the electronic computer was simplifiedtremendously by the standardization of the parts used to build it. Asthose parts became smaller they could be packaged together producingeven smaller devices with increased functionality operating faster thantheir predecessors. Boolean logic gates form the basic building blocksof the electronic digital computer. The use of Boolean logic isappropriate in this application because it is difficult to movecomplicated data on a signal voltage line. The analog electric computer,which held data as analog voltage signals, was not successful becausenoise in the voltage signals corrupts the data. In the analog computer'sfavor is the amount of information that is transmitted on one signal. Ananalog computer would have been very fast compared to the binarycomputer at that time.

[0003] Fiber optic cable is now the standard means of transmittinginformation over long distances mainly because it does not suffer fromcrosstalk, dispersion can be compensated for and information being movedoptically can be multiplexed in the wavelength domain. Wavelengthdivision multiplexing (WDM) allows signals transmitted at differentwavelengths (or colors) to be transmitted simultaneously down oneoptical fiber and operated on independently. Consequently, one opticalfiber can carry significantly more information than a metal wire basedon today's technology.

[0004] This advantage has been exploited by long distance bandwidthproviders but it has not gained acceptance for optical computingapplications. The concept of optical logic gates has been presented inU.S. Pat. No. 5,999,283. The patent describes a method of producingoptical logic gates. The gates presented combine semiconductor opticalamplifiers (SOA) and Mach Zehnder interferometers (MZI). The componentsit presents are based on Boolean logic which does not take advantage ofwavelength division multiplexing.

[0005] In U.S. Pat. No. 4,262,992 a general design is presented thatallows many different optical logic gates to share their footprint onthe same substrate. This device also uses an interferometer producingconstructive and destructive interference but in this case theinterference is controlled with electrodes making it possible toreconfigure the substrate as required.

[0006] In Choo, Detofsky and Louri, Sep. 10, 1999, Applied Optics Volume38, Number 26, p 5594 to 5604 an optical processor is presented in whichWDM and polarization effects are both used to enhance processing. Thissystem is limited to using bulk optics, which limit the size andtherefore complexity of the system. A two dimensional pixilated grid isused to polarization encode the data and wavelength is used todifferentiate between different sets of data. Data is manipulated withlogic gates that use polarization to attenuate the signal. Thisarchitecture cannot be used with fiber optic waveguides at this time dueto the difficulty of integrating small polarization controllingcomponents in the waveguides.

[0007] The field of optical computing is still developing and willlikely see applications in smaller scale data networks. One currentapproach to smaller scale networks uses a configurable networkarchitecture where destinations on the network are wavelength specificand the sources are tunable. This allows any source to selectively sendinformation to any location in the network provided that only one sourcetries to send data to one receiver at one time. This networkarchitecture is also limited in that the signals are not separated bywavelength until they reach their destination. Therefore, as the deviceis proposed in STARNET: A Multi-gigabit-per-second Optical LAN Utilizinga Passive WDM Star, Kazovsky, Poggiolini, Journal of LightwaveTechnology, Vol. 11, No. 5/6 1993, every receiver can see all of theinformation. The individual receivers must be tuned to read only theinformation that is intended for them. Also, the signals are attenuatedwhen they pass through the star coupler.

OBJECT OF THE INVENTION

[0008] In order to overcome these and other limitations of the priorart, it is an object of the invention to provide an optical digitallogic architecture that utilizes the wavelengths of light to performdata representation and manipulation. This architecture is referred toas the N-valued optical digital logic system. It has applications inoptical data storage and optical computing.

SUMMARY OF THE INVENTION

[0009] This invention relates to optical communication, data storage,and optical computing. It describes a means of processing and encodingdata in the optical domain. As an optical communications designinvention it describes an architecture supporting N wavelengths of lightrepresenting digital data in an N-valued logic system comprising:

[0010] a plurality of optical components, each component having an inputport and an output port and for operating on a light signal received atthe input port in accordance with a transfer function from a pluralityof predetermined transfer functions. The light within the signal at apredetermined wavelength of the N wavelengths corresponds to apredetermined value among the N values and wherein N is at least 2.

[0011] In the proposed N-valued optical digital logic system, thesetransfer functions are applied in the optical domain. Since the inputsignals and output signals are both optical signals, the output signalof a first gate can be used as an input signal to a second gate.

[0012] Additionally, the architecture supports two wavelengths, whereina first wavelength corresponds to a “0” and a second other wavelengthcorresponds to a “1”. It then uses a binary interface to convert the Nwavelength optical signal into an intensity encoded optical signalhaving two intensity levels representative of a 1 and a 0, respectively.

[0013] The optical logic gate transfer functions are given below. Thesegates can be combined to produce optical circuits. Alternatively, thesegates can be used for simpler optical applications.

[0014] The invention also allows the use of multiple wavelengths tostore data. That is, the data is stored in an appropriate medium inwhich one wavelength returns when a source hits it. Since a variety ofwavelengths can be returned the presence of the one returned wavelengthindicates the value of the data.

[0015] In accordance with another embodiment of the invention there isprovided an optical logic system having N symbols wherein each symbol isrepresented by a wavelength of light comprising:

[0016] a. an optical component including:

[0017] b. a first port for receiving a first optical signal at any ofthe N wavelengths representative of the N symbols;

[0018] c. an output port; and

[0019] d. an optical circuit for receiving the first optical signal atany of the N wavelengths, for varying the first optical signal inaccordance with a predetermined transfer function and for providing thesecond optical signal representative of one of the N symbols to theoutput port, the predetermined transfer function a same function foreach of the N wavelengths.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a schematic diagram of a Mach Zehnder Interferometer asis known in the art;

[0021]FIG. 2 is a schematic diagram of a semiconductor optical amplifieras is known in the art;

[0022]FIG. 3 is a schematic diagram of an O-AND optical logic gate;

[0023]FIG. 4 is a schematic diagram of an O-OR optical logic gate;

[0024]FIG. 5 is a schematic diagram of an O-NOR optical logic gate;

[0025]FIG. 6 is a schematic diagram of an O-NOT optical logic gate;

[0026]FIG. 7 is a schematic diagram of a prior art bandpass filter as isknown in the art; and,

[0027]FIG. 8 is a schematic diagram of an O-NAND optical logic gate.

DETAILED DESCRIPTION OF THE INVENTION

[0028] The invention relates to an architecture for use in designingoptical digital devices including an optical computer in which alllogical operations are accomplished in the optical domain withpredetermined wavelengths corresponding to predetermined values. Thearchitecture relies on a logic structure different from Boolean logic.The logic structure supports an N-ary logic system and is compatiblewith transfer functions obtainable using presently available opticalcomponents.

[0029] The proposed architecture takes advantage of improved technologyin fiber optics that allows the information to be encoded by wavelengthand/or by intensity. Currently, fiber optic networks can use 40wavelengths or more. In it's simplest form, an optical computer mightuse 2 wavelengths or channels to represent “0” and “1” in which only onewavelength is present at a time. Alternatively, more wavelengths areused increasing the amount of information that is wavelength encoded.For example, if 40 discrete wavelengths are used then information isrepresented by the combinations of the 40 -values from 0 to 39 with eachof the 40 wavelengths.

[0030] The proposed architecture allows the data to be encoded in theintensity domain and logic operations in the wavelength domain, whichforms a two-dimensional data representation and manipulation system.

[0031] In a proposed embodiment the architecture is implemented usingMach Zender interferometers (MZI) and semiconductor optical amplifiers(SOA). The MZI when combined with SOAs produce a component that can beused as a logic gate. Referring to FIG. 1, the MZI 100 and SOAs 111 aand 111 b work as follows: light enters the MZI 100 through the inputport 1 and is split equally. The two beams of light propagate throughwaveguides 2 and 3 respectively and each enters different SOAs 111 a and111 b. The SOAs 111 a and 111 b are capable of introducing a phase shifton the beams. When a second optical signal is presented at the inputport 4 a, it triggers SOA 111 a. When SOA 111 a is triggered, a phaseshift is not induced in light from the corresponding waveguide 2. Whenno light is presented to the input port 4 a, then a phase shift isinduced in the light signal from waveguide 2. The two beams are thenrecombined and exit the MZI 100 through the output port 5. If one of thebeams is phase shifted 180° relative to the other beam then adestructive interference condition results. The destructive interferencecondition causes no light to appear at the output waveguide 5. Whenthere is no phase difference between the two beams, for example ifneither beam has an induced phase shift, then the two beams addconstructively resulting in a light signal propagating at output port 5.

[0032] As shown herein, when an SOA is shown alone it does not behavethe way it does when integrated with in the MZI 100. Referring to FIG.2, a continuous light signal enters the SOA 200 via input port 6. When asecond light signal is provided via input port 7 the first signal loosesenergy and is attenuated. When the second light signal provided viainput port 7 has minimal intensity, the first optical signal isnominally attenuated and exits the SOA 200 via output port 8.

[0033] Referring to FIG. 3, an O-AND optical logic gate is shown forproducing the transfer function given in Table 1.1. There are numerousways of achieving this transfer function in an all optical device. FIG.3 shows a simple embodiment using an MZI with two SOAs. This devicecorresponds to the MZI 100 previously described. This gate 10 has twoinput ports 11 and 14 a and one output port 15. A first optical logicsignal X enters the MZI at the first input port 11. It will exit the MZI10 through the output port 15 provided that a second input signal Yhaving a predetermined value is present at the second input port 14 aentering the SOA. Within a broad range, the wavelength of the signalentering the SOA through input port 14 does not affect the operation ofthe device. When an optical signal exits the gate at the output port 15it will have the same wavelength as the signal at the first input port11, although it has been modulated by light entering at the second inputport 14. TABLE 1.1 O-AND N-valued Logic Gate Output X Y X O-AND Y InputPort 11 Input Port 14 Output Port 15 Y O-AND X 0 0 0 0 0 Y 0 0 X 0 0 0 XY X Y

[0034] Referring to FIG. 4, an O-OR gate 20 is shown for providing atransfer function in accordance with Table 1.2. This gate is implementedin any of a variety of different ways. The O-OR gate 20 relies on acontinuous input signal provided at input port 21. The continuous inputsignal is at a known wavelength that is the same wavelength as awavelength of a signal provided to input port 26. Light entering port 24modulates the continuous signal within the device producing an outputsignal at the output port of the MZI 25 a. This output port 25 a isconnected to the input port 25 of the SOA 28. When a light signal ispresent on the other input port 26 a to the SOA 28 then the outputsignal is substantially attenuated. When light below a predeterminedintensity enters the second input port 26 a then light entering from theinput port 25 a propagates to the output port 27 with nominalattenuation. TABLE 1.2 O-OR N-valued Logic Gate Output X Y X O-OR YInput Port 26 Input Port 24 Output Port 27 Y O-OR X 0 0 0 0 0 Y X 0 X 00 Y X Y 0 0

[0035] Referring to FIG. 5, an O-NOR gate 30 operates on light signalsbased on a transfer function given in Table 1.3. This gate isimplemented in any of a variety of different ways. The O-NOR gate shownis formed with a single SOA 30. An optical signal is provided at firstinput port 31. When an optical signal having sufficient intensity ispresented at a second input port 32 of the SOA 30 then light from thefirst input port 31 is substantially attenuated prior to exiting at theoutput port 33. When there is no signal of sufficient intensity at thesecond input port 32 then the optical signal entering the SOA from thefirst input port 31 exits the SOA at the output port 33 with minimalattenuation. TABLE 1.3 O-NOR N-valued Logic Gate Output X Y X O-NOR YInput Port 32 Input Port 31 Output Port 33 YO-NOR X 0 0 0 0 0 Y Y 0 X 00 X X Y 0 0

[0036] Referring to FIG. 6, an O-NOT gate 40 operates on light signalsbased on a transfer function given in Table 1.4. This gate isimplemented in any of a variety of different ways. The O-NOT gate shownis formed with a single SOA 40. A continuous signal is provided at firstinput port 41. When an optical signal having sufficient intensity ispresented at a second input port 42 of the SOA 40 then light from theinput port 41 is substantially attenuated prior to exiting at the outputport 43. When there is no signal of sufficient intensity at the secondinput port 42 then the optical signal entering the SOA from the firstinput port 41 exits the SOA at the output port 43 with minimalattenuation. TABLE 1.4 O-NOT N-valued Logic Gate Output X O-NOT X 0 X X0

[0037] Referring to FIG. 7, a bandpass filter 50 operates on lightsignals based on a transfer function given in table 1.5. It is a commoncomponent used in various DWDM applications and is known to thoseskilled in the art. An optical signal entering the input port 51 will beallowed to exit the bandpass filter at the output port 52 if and only ifthe wavelength of the input signal corresponds to the predeterminedwavelength. TABLE 1.5 Bandpass Filter Output Bandpass λ 1 Wavelength X(X)    0-λ 1 X 0 λ 1-λ 2 X X λ 2 and above X 0

[0038] Referring to FIG. 8, an O-NAND gate 60 operates on light signalsbased on a transfer function given in Table 1.6. This gate isimplemented in any of a variety of different ways. A first opticalsignal X is provided at first input port 61. This optical signal issplit into two separate optical signals with a coupler 62. The couplercauses some of the first input signal to enter a first input port 63 ofthe SOA 64. The remainder of the optical signal enters the first inputport 68 a of the MZI 65. When a second optical signal Y havingsufficient intensity is presented at a second input port 66 of the SOA64 then light from the first input port 63 is substantially attenuatedprior to exiting at the output port 67. When there is no signal ofsufficient intensity at the second input port 66 then the optical signalentering the SOA from the first input port 63 exits the SOA at theoutput port 67 with minimal attenuation. The optical signal at inputport 68 a will exit the MZI 65 through the output port 71 provided thata second input signal is present at the second input port 67 a enteringthe SOA 72. Within a broad range, the wavelength of the signal enteringthe SOA through input port 67 a does not affect the operation of thedevice. When light exits the gate at the output port 71 it will have thesame wavelength as the signal at the first input port 61. TABLE 1.6O-NAND N-valued Logic Gate Output X Y X O-NAND Y Input Port 61 InputPort 66 Output Port 71 Y O-NAND X 0 0 0 0 0 Y 0 Y X 0 X 0 X Y 0 0

[0039] As basic optical logic elements the gates can be combined toproduce different digital optical circuits. Conceptually, this isanalogous to the use of Boolean logic gates to represent the operationof a digital electrical circuit. However, they are not equivalentbecause the optical logic gates work with various wavelengths and theBoolean electrical logic gates work with only two states (“on” or“off”). The optical logic gates have been given names that that areconsistent with Boolean logic gates. An “O” has been added as a prefixto the gate's name to distinguish these optical logic gates from theBoolean gates. These gates can be combined to produce optical circuitswhose function is analogous to similar electrical circuits.

[0040] The analogous electrical circuits to these circuits provide thearchitecture used to design electrical binary computers. The N-valuedlogic circuits provide the architecture used to design an N-valued basedcomputer and other N-valued optical digital devices. The proposedimplementation of the N-valued digital system uses optical signals withdifferent wavelengths to represent different data values however anN-valued computer need not be optical. Quantum states, for example, canbe used to implement the current N-valued digital system.

[0041] The design of a complex N-valued device based on the proposedarchitecture requires a means of describing the mathematical operationsalgebraically. The algebra is based on a structure which is defined suchthat (W, +, −, “, ‘, 0) with two binary operators + and −, two unaryoperators “, and ‘, and one distinguishing element 0 and a set W alongwith a set of postulates. The postulates include closure, commutativelaws, associative laws, distributive laws, identities, subsetcomplements, global complements and conversion. The set W contains Nelements where N can be any whole number. We denote W={C₀, C₁, C₂ . . .C_(N)} with C₀, C₁, C₂ . . . C_(N) ε W.

[0042] The closure postulate states that set W is closed with respect tothe unary operators “ and ‘ and binary operators + and −.

[0043] The commutative laws state that for all a, b ε W.

a+b b+a but a+b=a+(b+a)

a−b b−a but a−b=(a+b)−b

=a−(a−b)

[0044] The associative laws state that:

a+(b+c)=(a+b)+c

a−(b+c)=(a−b)+c

[0045] The distributive laws state that:

a+(b−c)=(a+b)−(a+c)

a−(b+c)=(a−b)+(a−c)

(a−b)+c=(a+c)−(b+c)

(a+b)+c=(a+c)+(b+c)

a−(b−c)=(a−b)−(a−c)

[0046] The identity postulate states that the distinctive element 0 ε Wis an identity element with respect to binary operators + and − forevery a ε W such that,

0+a=0

a+0=0

a−0=0

0−a=c where c ε W

[0047] Also,

a+a=0

a−a=0

[0048] The subset complement postulate states that for any element in atwo element subset w ε W with W−{0, a} there corresponds an element ofa′ with w such that

a″=0

0′=a

[0049] The complement or global complement postulate states that for anyelement a in W there corresponds an element a″ in W such that

a″=0

0″=C, C is any element in W

[0050] The conversion postulate states that for any element a ε W thereis a conversion such that

a−>b, b εW

[0051] While it is known that N-valued logic, also referred to asswitching algebra, is not unique, numerous other embodiments may beenvisaged without departing from the spirit and scope of the invention.

1. An architecture supporting N wavelengths of light representingdigital data in an N-valued logic system comprising: a plurality ofoptical components, each component having an input port and an outputport and for operating on a light signal received at the input port inaccordance with a transfer function from a plurality of predeterminedtransfer functions; wherein light within the signal at a predeterminedwavelength of the N wavelengths corresponds to a predetermined valueamong the N values and wherein N is at least
 2. 2. An architectureaccording to claim 1, wherein the transfer function within the N-valuedlogic system is realized in the optical domain.
 3. An architectureaccording to claim 2, in which an output port of one component isoptically coupled to an input port of another component.
 4. Anarchitecture according to claim 2, wherein N=2, wherein a firstwavelength corresponds to 0 and a second other wavelength corresponds to1 and comprising: a binary interface to convert the N wavelength opticalsignal into an intensity encoded optical signal having two intensitylevels representative of a 1 and a 0, respectively.
 5. An architectureaccording to claim 2, wherein the plurality of predetermined transferfunctions includes: an O-AND gate for providing a transfer function frominput signals X and Y to an output signal C_(out) according to thefollowing table: X Y C_(out) = X O-AND Y 0 0 0 0 Y 0 X 0 0 X Y X


6. An architecture according to claim 2, wherein the plurality ofpredetermined transfer functions includes: an O-OR gate for providing atransfer function from input signals X and Y to an output signal C_(out)according to the following table: X Y C_(out) = X O-OR Y 0 0 0 0 Y X X 00 X Y 0


7. An architecture according to claim 2, wherein the plurality ofpredetermined transfer functions includes: an O-NOT gate for providing atransfer function from input signal X to an output signal C_(out)according to the following table: X C_(out) = O-NOT X 0 X X 0


8. An architecture to claim 2, wherein the plurality of predeterminedtransfer functions includes: an O-NOT gate for providing a transferfunction from input signals X and Y to an output signal C_(out)according to the following table: X Y C_(out) = X O-NOR Y 0 0 0 0 Y Y X0 0 X Y 0


9. An architecture according to claim 8, wherein the plurality ofpredetermined transfer functions includes: an O-NAND gate, having asimilar transfer function to the O-NOR. X Y C_(out) = X O-NAND Y 0 0 0 0Y 0 X 0 X X Y 0


10. An architecture according to claim 1, wherein the plurality oftransfer functions comprising: an O-NAND gate, O-NOR gate, O-AND gate,O-NOT gate and O-OR gate.
 11. An optical logic system having N symbolswherein each symbol is represented by a wavelength of light comprising:an optical component including: a first port for receiving a firstoptical signal at any of the N wavelengths representative of the Nsymbols; an output port; and an optical circuit for receiving the firstoptical signal at any of the N wavelengths, for varying the firstoptical signal in accordance with a predetermined transfer function andfor providing the second optical signal representative of one of the Nsymbols to the output port, the predetermined transfer function a samefunction for each of the N wavelengths.
 12. A system implementing thearchitecture of claim 1, for supporting all optical logic comprising: aplurality of optical logic devices operating on a plurality of lightsignals of any of the N different wavelengths to provide logicalcombinations of the plurality of light signals in a predeterminedfashion other than coupling of the light signals and filtering ofpredetermined wavelengths from the light signals; an optical logicdevice operating on a second light signal of one of the N differentwavelengths to provide an optical output signal being the inverse of thesecond light signal in accordance with a predetermined transferfunction; and wherein the predetermined transfer function is analogousfor light signals of any of the plurality of wavelengths provided to agiven device.
 13. An optical computing device comprising: an opticalinput port; and a plurality of O-NOR, O-AND, O-NOT, O-NAND and O-ORlogic gates combined such that the device's transfer function isconfigurable from the optical input port.
 14. An optical computingdevice (OCD) according to claim 14 with an output port where the outputport is coupled to the optical input port of another OCD.